Athletes warned: vitamin D could be a muscle killer

February 21, 2014

Athletes hunting for that competitive edge, be warned – vitamin D supplements might actually increase muscle damage instead of reducing it, according to a US study.

Researchers from the Appalachian State University in North Carolina found that taking vitamin D2 supplements decreased levels of vitamin D3 and increased muscle damage in athletes after an intense weight lifting session.

The study measured the effects of six weeks of vitamin D2 supplementation in NASCAR pit crew athletes, particularly regarding levels of exercise-induced muscle damage and the delayed onset of muscle soreness.

Researchers separated the athletes into two groups, the first of which consumed 3800 international units a day of a plant-based vitamin D2, while the second had a placebo. The supplement was derived from Portobello mushroom powder that had been irradiated with ultraviolet light to convert the ergosterol in the mushrooms to vitamin D2 (ergocalcifoerol).

The study was designed to test the hypothesis that the B2 supplement would improve performance by reducing inflammation and aiding in recovery.

But, in a surprise finding, the researchers discovered this was not the case, and that the supplement actually caused damage.

Lead researcher Dr David Nieman said this was the first time research had shown that vitamin D2 supplementation was associated with higher muscle damage after intense weight lifting.

“When the sun hits our skin it turns into vitamin D3. The body is used to that,” Dr Nieman said. “High vitamin D2 levels are not a normal experience for the human body. Taking high doses of vitamin D2 caused something to happen at the muscle level that isn’t the best for athletes.”

Researchers have been studying the benefits of vitamin D for athletes since the middle of last century, when a European scientist claimed athletes who were exposed to sunlamp sessions performed better in winter months.

Dr Nieman said that just about everyone has lower levels of vitamin D during the winter, and that restoring vitamin D levels in older people improves their muscle function. But, he added, it was yet to be determined if this held true for younger adults.

“We were interested in seeing if increasing vitamin D in pit crew athletes who train heavily in the off-season would improve their muscle and immune function,” Dr Nieman said. “While vitamin D2 levels in the blood increased, we found that levels of D3 decreased and, to our surprise, those taking vitamin D2 didn’t have just a little more muscle damage – they had a lot more damage.”

Dr Nieman said he suspected that vitamin D2 caused something to occur in the muscle that worsened damage following stressful exercise.

As a result of the study, he said it was not recommended that athletes who lift weights or exercise a lot use vitamin D2 supplements.